1. Field of the Invention
The present invention relates to a process for producing a perfluorinated vinyl ether having an ester group which has the formula EQU CF.sub.2 .dbd.CFOCF.sub.2 (A).sub.p (CF.sub.2).sub.q CO.sub.2 R
wherein A represents a C.sub.1 -C.sub.10 divalent perfluorinated radical; p represents 0 or 1; q represents 0 or 1 to 3; and R represents an organic radical.
Description of the Prior Art
The perfluorinated vinyl ethers are useful as monomers for producing fluorinated polymers. The perfluorinated vinyl ethers obtained by the process of the present invention can be used as comonomers for forming cure-sites in fluorinated polymers and as monomers for producing fluorinated polymers having special functions, and can be used in various fields.
The processes for producing the perfluorinated vinyl ethers having an ester group are disclosed in Japanese Patent Publication No. 22327/1970 and British Pat. No. 1,145,445. The conventional processes include the reaction of perfluorodiacyl fluoride with hexafluoropropylene oxide to produce perfluoro(2-methyl-3-oxa-alkane) diacyl fluorides. In the second step, the diacyl fluoride is esterified with an alcohol preferably with methanol to produce the diester. The diester is then, either saponified with an anhydrous methanol solution of potassium, sodium or cesium hydroxide to give the di-metal salt, or converted by a reaction with water to the diacid which is then, neutralized with an aqueous solution of one of said hydroxides. Then, the di-metal salt is converted by a thermal decomposition, to the mono-metal salt and the resulting mono-metal salt is hydrolyzed to give the perfluorinated vinyl ether carboxylic acid and then, the product is converted by an esterification to give the perfluorinated vinyl ether having an ester group.
In the conventional processes, many reaction steps are required and the yield in the thermal decomposition of the di-metal salt of perfluorodicarboxylic acid is remarkably low such as about 25% disadvantageously. Moreover, the starting material of di-metal salt of dicarboxylic acid and the product of mono-metal salt of vinyl ether carboxylic acid are solid to be disadvantageous from the viewpoint of the operation for the reaction.
As described above in the conventional processes, an esterification as the reaction of the perfluorinated vinyl ether having --COOH group with an alcohol or a tranesterification has been usually performed for producing perfluorinated vinyl ether having an ester group.
In these conventional processes, the esterification or the transesterification is an equilibrium reaction whereby a large amount of an alcohol is required and it is difficult to attain high conversion within a limited time. The conventional processes have disadvantage of preventing an increase of the space time yield in an industrial operation. Moreover, the conventional processes have disadvantages of a use of an acid or base catalyst and a reaction temperature being a refluxing temperature of an alcohol from the viewpoint of protecting a highly reactive perfluorinated vinyl ether group.
Recently, it has been proposed to produce the perfluorinated vinyl ether having an ester group by using a compound having an ester group as the starting material, for example, the thermal decomposition of a perfluorinated acyl fluoride or metal-salt of perfluorinated carboxylic acid having an ester group disclosed in Japanese Unexamined Patent Publication No. 78827/1977 and 105118/1977 and British Pat. No. 1,532,172 and the reaction of the specific fluorinated diester with lithium chloride disclosed in Japanese Unexamined Patent Publication No. 89603/1977.
In these recent processes, many kinds of by-products are disadvantageously produced to be low reaction efficiency and a purification of the object product is not disadvantageously easy.
In order to apply the conventional process in an industrial scale, many difficult operations are required. It has not been attained to produce a perfluorinated vinyl ether having an ester group in an industrial scale in high efficiency.
The inventors have studied to produce the perfluorinated vinyl ethers having an ester group in high yield by a simple process. As the results, the following important facts have been found.
When the asymmetric diacyl fluoride having ##STR2## group at one end and FOC--CF.sub.2 -- group at the other end is pyrolyzing at about 200.degree. to 350.degree. C. in a vapor phase, a vinyl etherification is surprisingly performed without losing --COF group at the other end to obtain smoothly and advantageously the perfluorinated vinyl ether having --COF group. When an alcohol is reacted with the perfluorinated vinyl ether having --COF group, the object product of the perfluorinated vinyl ether having an ester group can be selectively obtained in high efficiency.